Ultrasonic doppler blood flowmeter

Abstract

An ultrasonic Doppler blood flowmeter measures the velocity of blood flow at an arbitrary position of the body of a subject by making use of Doppler shift of an ultrasonic echo signal. The echo signal including Doppler shift from the blood flow of the body is detected in phase on the basis of standard reference signal, and the distance to an intended position is extracted from the phase detected signal and is integrated, and the direct-current component or ultraflow frequency component of the Doppler shift signal obtained from the integrator means is fed back negatively to the integrator means. As a result, the echo signal components of the body tissues are removed, and the frequency of blood flow only can be analyzed, so that an accurate blood flow information may be obtained.

What is claimed is: 
     
       1. An ultrasonic Doppler blood flowmeter adapted for measuring the flow of blood through a body of a subject, said flowmeter comprising, at least, an ultrasonic transmission means for transmitting ultrasonic pulses into the body of a subject; an ultrasonic reception means for receiving echo signals reflected within the body; a drive circuit means for generating ultrasonic pulses to be transmitted by said ultrasonic transmission means; a transmission timing signal circuit means for generating timing signals used to generate ultrasonic pulses by means of said drive circuit means; a phase detecting means for detecting the amplitude and phase of each of said echo signals obtained by said ultrasonic reception means; a reference signal generation circuit means for generating a reference signal serving as the reference for the frequency and phase of a transmission signal of said drive circuit means and a reference signal for frequency and phase when detecting the phase of each of said echo signal; a gate signal generating circuit means operatively connected to said transmission timing signal circuit means and to said reference signal generating circuit means for generating a gate signal of variable period at a time corresponding to an echo signal from a desired position; a control means for controlling the transmission therethrough of the phase signal detected by said phase detecting means in response to said gate signal; an integrating circuit means for obtaining a Doppler shift signal by integrating the phase signal transmitted through said control means; a sample and hold circuit means for temporarily holding the integrated result obtained by said integrating circuit means; a variable gain feedback circuit means for negatively feeding back a direct-current component of an ultra-low frequency component of the Doppler shift signal obtained by said integrating circuit means or held by said sample and hold circuit into said integrating circuit means; and a feedback gain control circuit means for controlling the gain of said feedback circuit in proportion to the period of said ultrasonic pulses or in inverse proportion to the time width of said gate signal generated by said gate signal circuit means. 
     
     
       2. An ultrasonic Doppler blood flowmeter as recited in claim 1, wherein said feedback circuit means is consisting of a low pass filter using an integrating circuit means and a gain variable amplifier for controlling the gain thereof. 
     
     
       3. An ultrasonic Doppler blood flowmeter as recited in claim 1, wherein said feedback circuit means is consisting of a low pass filter using an integrating circuit means and a time constant control circuit means for controlling the time constant of said integrating circuit means. 
     
     
       4. An ultrasonic Doppler blood flowmeter as recited in claim 1, wherein said feedback circuit means is consisting of a low pass filter using an integrating circuit means and a chopper circuit means which turns the input of said integrating circuit means on and off. 
     
     
       5. An ultrasonic Doppler blood flowmeter as recited in claim 1, wherein said feedback circuit means is connected to said control means such that said feedback signal from the feedback circuit means is fed back to the input terminal of said control means. 
     
     
       6. An ultrasonic Doppler blood flowmeter as recited in claim 1, wherein said ultrasonic transmission means and said ultrasonic reception means together comprise one ultrasonic probe. 
     
     
       7. An ultrasonic Doppler blood flowmeter as recited in claim 1, wherein said control means comprises an analog switch.